On Thu, 20 Feb 2003, Suresh S wrote:
>Hi,
>>>> gen_event:call(EntMgr, Handler, Req) -->
>>> M:handle_event(Req, S)
>>>> No, a call is handled in M:handle_call(Query,State)
>>i mean to ask for handle_call only , but in a hurry i
>mistyped
>>Any how in case of M:handle_call(Req, S)
>How do we pass Handler = { M, Id }
>>what is the need for Id?
>how do i pass the handler i have to handle?
>From the gen_event reference manual:
"Handler is the name of the callback module Module or a
tuple {Module,Id}, where Id is any term. The {Module,Id}
representation makes it possible to identify a specific
event handler when there are several event handlers using
the same callback module."
If you only have one instance of a specific handler, then
Handler becomes simply the module name.
The {Module,Id} construct is for the case that you have lots
of instances of similar handlers, and it's not practical, or
even desired, to implement a module for each instance. Id
can be anything that helps you tell the different handlers
apart in your application.
A very common way to identify the handler is to use the
?MODULE macro. Example from the OTP EVA application:
module eva_snmp_adaptation.erl:
start() ->
gen_event:add_handler(alarm_handler, ?MODULE, []),
register_events([{clear_alarm, alarmCleared,
snmpTrap, "standard trap",
{?MODULE, clear_alarm}}]).
register_events(Events) ->
gen_event:call(alarm_handler, ?MODULE,
{reg_events, Events}).
handle_event({send_event, Event}, S) ->
case mnesia:dirty_read({eva_snmp_map,
{event, Event#event.name}}) of
[#eva_snmp_map{val = Data}] ->
send_event(Data, Event);
_ ->
ok
end,
{ok, S};
...
handle_event(_, S) ->
{ok, S}.
handle_call({reg_events, Events}, S) ->
#state{event_struct = EStruct,
next_event_index = Index} = S,
{NEStruct, NIndex} = reg_events(Events, EStruct, Index),
{ok, ok, S#state{event_struct = NEStruct,
next_event_index = NIndex}};
... where events are sent from eva_server.erl using
gen_event:sync_notify(alarm_handler, {send_event, Event})
/Uffe
--
Ulf Wiger, Senior Specialist,
/ / / Architecture & Design of Carrier-Class Software
/ / / Strategic Product & System Management
/ / / Ericsson AB, Connectivity and Control Nodes